Fluid mixing apparatus

ABSTRACT

A fluid mixing apparatus having means for producing vortex-like motions of the fluids introduced therein, one embodiment of such an apparatus, for example, using two concentrically mounted inner and outer members, preferably cylindrical, moveable relative to each other at rotational speeds such as to produce the desired vortex-like motions of the fluids introduced into the region therebetween. In one embodiment thereof, the vortex-like motions may be obtained at relatively low rotational speeds by the use of V-shaped grooves on the inner member. In addition, suitable means can further be used to generate a de-stabilizing force for the fluids in a direction substantially perpendicular to the velocity streamlines thereof to further enhance the mixing effectiveness and to improve the quality of the mix, such de-stabilizing force in one embodiment, for example, being generated by the application of an electric field across the region between the inner and outer members.

The Government has rights in this invention pursuant to Grant No.DI-38249 and IPA-0010 awarded by the National Science Foundation.

This is a continuation of application Ser. No. 584,985, filed June 9,1975, now abandoned.

This invention relates generally to fluid mixing apparatus and, moreparticularly, to apparatus for mixing viscous reacting liquids.

BACKGROUND OF THE INVENTION

The effective mixing of two or more fluid components, particularly whereone or more of such fluids is relatively highly vascous and reactive, issometimes difficult to accomplish. For production line operation, as ina molding process, a product mix of suitable quality must be produced ata reasonably fast rate so that the ultimate molded unit can befabricated at an economically profitable rate. For example, in themixing of some viscous materials, which react chemically to form apolymer such as polyurethane, the mixing apparatus for use in a moldingprocess, often must be arranged to supply a discrete quantity of aproduct mix on a discontinuous, or batch, basis, the quality of the mixbeing required to be sufficiently high that the quality of the moldedproduct is not deleteriously affected.

Moreover, the mixing rate must be high enough so as to provide a goodquality of mixing before the reactive fluid compounds undergo asignificant amount of reaction in the mixing chamber. It is essentialthat the mixed liquid remain at a sufficiently low viscosity until themold is completely filled. Since the ultimately desired physicalproperties of the mixed material, such as its low-temperature,flexibility and modulus characteristics, depend on the molecular weightsof the reacting liquids and thus, on their viscosities, an effectivemixing apparatus should not be limited by the viscosity characteristicsof the liquid components being mixed.

Further, any production system must be such that the desired productionrate should be achieved at a reasonable cost, the size and complexity ofthe device being such that installation and maintenance expenses can beheld to reasonable levels.

A common problem with many continuous and certain batch mixers is thatthey must be periodically cleaned to prevent an over-accumulation ofreacted material from adversely affecting the performance of theapparatus. Often, because of the complicated geometr of the mixer, thecleaning operation must be laboriously performed by hand, the overallcosts thereby increasing due both to the additional labor required andto the decreased oproduction which results because of machine down time.

Discussion of the Prior Art

Conventional mixing apparatus usually makes use of rotary blades, spiralribbons or paddles which mix input liquids in suitable bowl-like ortubular containers. Such systems not only often provide relatively lowquality product mixes at low production rates but also the cleaningproblems involved are extremely troublesome and increase the coststhereof in production applications.

One mixing apparatus which has been suggested by the prior art forproviding more efficient operation has been described in U.S. Pat. No.3,706,515 issued on Dec. 19, 1972 to Keuerleber et al. Such apparatusrepresents an attempt to avoid the build-up of reacted material and toincrease the batch quantity; i.e., the "shot capacity" of the process.In accordance therewith, each of the liquids is supplied to a highpressure nozzle to form inpinging liquid streams for providingappropriate intermingling thereof so that effective primary mixing isachieved. At the end of each cycle, the material in the mixing chamberis forced out by a moveable ram. A blast of high pressure air is thenused to clear out the two nozzles and prevent clogging. Although such asystem has a relatively good shot capacity when used in batchprocessing, the requirement for high pressure equipment makes the systemrelatively complex and expensive to construct and maintain. Moreover,because the input fluids must be forced under pressure through thenozzles, the apparatus is unable to handle liquids of very highviscosities and, therefore, has a limited range of applications.

Another apparatus of the prior art has been made and sold by USMCorporation and is described in the article "Liquid Injection Molding:Output Control Automation Opens Big Markets" by R. P. Titlebaum,appearing in Plastics Machinery & Equipment Magazine of 1974, additionaldescriptions of the uses and structures thereof also being found in U.S.Pat. Nos. 3,409,174; 3,448,967; 3,632,022 and 2,794,301. Basically, theapparatus comprises a mixing head which includes a cylindrical chamberhaving inlet and outlet valves at one end and a moveable ram at theother. Mixing is accomplished by the rotation of an impeller located atthe bottom of the chamber. The impeller is rotated at relatively highspeeds up to 10,000 to 13,000 r.p.m. and the moveable ram isappropriately raised while the components to be mixed are pumped intothe chamber in the proper ratio. When the ram is raised to its maximumheight, the outlet valve is opened to permit the injection of mixedmaterial into a mold, and when all of the input components have beenpumped into the chamber, the inlet valves are closed and the ram islowered to force most of the remaining material out of the chamber andinto the mold.

In order to reduce the frequency of cleaning thereof, a diluent is addedat the beginning of the cycle to retard the chemical reaction. While theUSM machine is not limited to low viscosity materials as the impingementmixer in the above discussed Keuerleber patent, the residence time ofthe input liquids in the mixing chamber is longer than that in theimpingement mixer and the production yield is relatively low. Even ifone adopts a combined mixing system consisting of the impingement andimpeller types, as has been suggested, such a combination undulycomplicates the mixing apparatus and does not overcome the basicproblems associated with laminer mixing as discussed below.

Other mixing apparatus which might be utilized for two component fluidmixing can be found in U.S. Pat. No. 2,857,144 issued on Oct. 21, 1958to J. F. Gurley, Jr. et al and variations thereof as shown in U.S. Pat.Nos. 2,969,960; 2,970,817 and 3,420,506 all issued to J. F. Gurley onJan. 31, 1961, Feb. 7, 1961 and Jan. 7, 1969 respectively. Suchstructures show conical or cylindrical chambers which usecorrespondingly shaped rotating inner elements having various forms ofprojections on the surface thereof, the components to be mixed beingintroduced in the gap between the outer surface of the inner member andthe inner surface of the outer chamber member. The gap therebetween isrelatively small in comparison to the radial dimensions of such membersand the apparatus would appear to provide relatively low productionrates and less effective mixing than may be required in manyapplications. Moreover, the conically shaped chambers and inner membersthereof appear to be particularly difficult to construct so that thecosts would appear to be relatively high for some applications.Moreover, while such patents do not discuss the effectiveness of suchdevices in handling relatively viscous liquids, the small gaps usedtherein would appear to make the handling thereof relatively difficult.

Most of the mixing devices discussed above accomplish mixing byso-called "laminar" mixing techniques. Laminar mixing occurs when thefluid is so viscous that the Reynolds number characterizing the flowthereof is low. In this case, the mixing of two fluids, for example, isaccomplished by subjecting the fluid components to distortionaldeformation and increasing the interface area of contact between the twofluid components for a given volume thereof. This type of laminar mixingis most efficient when the fluid interface is perpendicular tostreamlines of the fluids. However, as the fluids are sheared, theinterface therebetween tends to become parallel to the streamlinesthereby decreasing the mixing efficiency.

More effective laminar mixing can be promoted by creating vortex-likemotions, or secondary flows of the fluids. A careful investigation ofthe fluid mechanics of many of the prior art devices discussed aboveshows that the purported operations thereof appear to be contrary tothose predicted by theoretical models. Furthermore, regardless of howvortex-like motions are generated, the mixing efficiency per unit powerconsumed decreases with mixing time because the interface between thefluids tends over the course of time to become parallel to thestreamlines. Therefore, a good mixer must be able to generate vortexmotions efficiently for good laminar mixing and at the same time must beable to produce an additional fluid motion so as to make the interfacebecome perpendicular to the streamlines.

BRIEF SUMMARY OF THE INVENTION

This invention includes techniques for mechanically generatingvortex-like motions of the fluid components to produce good mixing, aswell as further techniques for maximizing the efficiency of mechanicalmixing by utilizing the instability of fluid motion induced by thegeneration of a suitable de-stabilizing force, as by the use of anelectric field in a manner described in more detail below. Further, theinvention can be suitably embodied in apparatus which can accomplish thelatter mode of mechanical-electrical hybrid mixing. In accordance withthe invention, an effective high quality mixing of multi-componentfluids can be provided at relatively low cost, which mixing can beaccomplished with a residence mixing time which is shorter than thatprovided by any presently known commercial processes. Such high qualitymixing can be provided at relatively high production rates on acontinuous or a batch basis even when used with fluids having very highviscosities. In accordance with one exemplary embodiment, the mixingapparatus of the invention includes an outer cylindrical member and aninner cylindrical member which is concentrically mounted therein. Thesurface of the inner cylinder may be smooth for ease of cleaning or mayhave a plurality of V-shaped grooves formed therein. When the innercylinder is smooth, vortex-like motion is generated when the Taylornumber is greater than a critical value, a phenomenon well-known in thefield of fluid mechanics. When the inner cylinder is grooved,vortex-motion is substantially immediately generated at much lowerrotational velocities than those required for a smooth inner cylinderwhen the fluids to be mixed are introduced into the region between theV-grooved inner cylinder and the outer cylinders. A relative radial andtangential motion is provided therebetween so that the grooves produce avortex-like motion of the fluids as they flow along such region.

In a preferred embodiment of the invention using V-shaped grooves, forexample, it has been found that a high quality product mix can beachieved at relatively high production rates when the mean distance fromthe inner surface of the outer cylinder to the surface of the innercylinder is approximately comparable to the mean radius of the innercylinder. Further, in a preferred embodiment of the invention, usingV-shaped grooves, the quality of product mix can be effectively enhancedwhen the ratio of the mean distance from the inner surface of the outercylinder to the surface of the inner cylinder is substantiallycomparable to the axial length of one groove.

In another preferred embodiment of the invention, it is found that themixing quality can be even further improved if a suitable de-stabilizingforce can be generated for the fluids in a direction which issubstantially perpendicular to the velocity stream lines of the fluids.Such a force can be obtained, for example, by the generation of anelectric field in the region between the inner and outer cylindricalmembers which field acting in combination with the vortex-like motionsprovides an enhanced overall mixing process even when the innercylindrical member has a relatively smooth, non-grooved surface. In suchan embodiment the de-stabilizing force which is thereby generatedprovides an effective change in the direction of the fluid interface sothat it no longer tends to assume a perpendicular orientation withrespect thereto.

Thus, the invention provides an apparatus having a relatively highproduction capacity which is better than most prior art devicesdescribed above while at the same time the apparatus is mechanicallyrelatively simple to manufacture and maintain and is capable of handlingfluids having a wide range of viscosities.

The invention can be described in greater detail with the held of theaccompanying drawings wherein:

FIG. 1 shows a diagrammatic view of the liquids interface which resultwhen two liquids are introduced into a mixing apparatus;

FIG. 2 shows the diagrammatic view of the formation of laminar layerswhen the liquids of FIG. 1 are mixed;

FIG. 3 shows one embodiment of the invention which uses a smooth innercylindrical member;

FIG. 4 shows an alternative embodiment of the invention which has agrooved inner cylindrical member;

FIG. 5 shows a further alternative embodiment of the structure of FIG. 4which uses a continuous helical groove on the inner cylindrical member;

FIGS. 6 and 7 show alternative forms of the structures of FIGS. 4 and 5;and

FIG. 8 is a graph illustrating the mixing effectiveness when usingmixing apparatus in accordance with various embodiments of theinvention.

Many processes in which the mixing of multiple components is required,such as in polymer processing, utilize the techniques of dispersivemixing wherein both a change in the spatial distribution of thecmponents and a change in the shape and size thereof occurs. In polymermixing such dispersive mixing can involve the breakdown of the size ofpolymeric particles (called "intensive" mixing) or can involve theinducing of shear deformation and the increasing of the interfacial areabetween the multiple components (called "extensive" mixing). The lattertechnique is often used in the mixing of two liquids which haverelatively high viscosities, as in polymer processing, the shearing ofthe liquid components to maximize the surface-to-volume ratio producinga laminar mixing.

Thus, as shown for example in the plan, diagrammatic view of FIG. 1, oftwo defined components "A" and "B" are introduced into the regionbetween an inner cylinder 10 and an outer cylinder 11, as shown, aninterface contact area "C" is initially formed therebetween. If theinner cylinder is rotated in the direction, for example, as shown by thearrow 12 in FIG. 2, shear deformation of the liquids occurs and aplurality of laminar layers thereof are generated, as shown, the numberof layer increasing as the rotating motion continues. Such motionincreases the surface area of contact between the liquids and provides asuitable mixing operation as desired.

In order to maximize the efficiency, the interface between the fluidcomponents should be as perpendicular as possible to the streamlines offluid motion, However, the nature of fluid motion is such that withincreased motion the interface becomes more and more parallel to thestreamlines. In order to improve the mixing efficiency, appropriatemeans are provided for supplying a suitable de-stabilizing force forchanging the direction of the interface relative to the velocitystreamlines of the fluids so that such direction is brought closer to adirection which is perpendicular to the streamlines.

As used herein, the term "de-stabilizing force" means a force caused bydeformations of the fluid materials which in turn tends to cause furtherdeformations thereof so that, in effect, an ever-increasing build-up ofdeformations occurs. Such a de-stabilizing force can be generated byutilizing an external agent for interacting with a selected property ofthe fluid materials. So long as the magnitude of the selected propertyis different for each of fluid materials involved, a de-stabilizingforce can be generated. Thus, for example, if the selected property isthe electrical conductivity of the fluid materials which are to bemixed, so long as the conductivities of the fluids are different, anelectric field applied in the appropriate direction to the fluids willcause the generation of the required de-stabilizing force which willthereupon enhance the overall mixing quality as desired.

In one embodiment of the invention depicted in FIG. 3, an innercylindrical member 21 is mounted concentrically with respect to an outercylindrical member 20. Inner member 21 is attached to a rotable shaft 22so as to rotate at a rotational velocity as shown, by a suitablerotating source, such as a motor (not shown).

A first tubular input feed line 23 extends through the wall of outercylinder 20 at one end thereof and in turn is connected to a first fluidsource 24 via a pump 25 and valve 26. A second tubular input feed line27 also extends through such wall at the same end as feed line 23 and isconnected to a second fluid source 28 via a pump 29 and valve 30.Accordingly, a fluid from such sources is appropriately introduced intothe region between the inner wall of outer cylinder 30 and the externalsurface of inner core cylinder 21.

When the fluid components are introduced at input feed lines 23 and 27,mixing is accomplished by rotation of the inner core member at anappropriate rotational velocity. The radius of the inner core member inthe configuration shown in FIG. 1 is designated as r and the gapdistance from the inner wall of outer cylinder 20 to the radius isdesignated as a. If the kinematic viscosities V₁ and V₂ of the inputfluid components are assumed to be substantially the same, asrepresented by V, the physical process by which the mixing occursdepends on the rotational velocity ω, together with the above parametersin accordance with the value of the Taylor number, as set forth below:##EQU1##

Mixing is accomplished generally by shear deformation of each of thefluid components which results essentially in the formation of amulti-layered helical sandwich of the fluid components such as showndiagrammatically in FIG. 2. As the rotational velocity increases to arelatively large value, the layers become relatively thin so thatdiffusion of the components takes place and mixing occurs.

At relatively low velocities, the shear action tends to be non-uniform,that is, the shear action nearer the rotating inner cylinder tends to bebetter than the shear action nearer the surface of the outer cylinder.In order to provide a more uniform shear action and, hence, a moreuniform mixing throughout the entire region between the cylinders, it isdesirable to provide a motion of the fluids such that the fluids move ina vortex-like motion between the surfaces as shown by the vortices 32 inFIG. 3. Such motion is effectively produced if the velocity is increasedto a value such that the Taylor number exceeds a critical value.

However, even though improvement in mixing uniformity is accomplished byutilizing rotational velocities above a critical Taylor number, thehigher velocities tend to produce a fluid interface which, with time,becomes more and more parallel to the velocity streamlines of fluidmotion. In order to enhance the mixing process, in accordance with theinvention, an appropriate de-stabilizing force is provided to cause amovement of the interface such that it will move in a direction whichtends to be perpendicular to the streamlines. Such a force may be onewhich acts as a surface force or a body force upon the fluids involved.For example, an electric field which is applied in a directionsubstantially perpendicular to the velocity streamlines of the fluidscan supply such a surface force if the electrical conductivities of thefluids involved are different. Other means can also be used forsupplying such forces. For example, with suitable fluids, a magneticfield can be applied in the appropriate direction perpendicular to thestreamlines to act upon the magnetic characteristics of the fluids andproduce an effective body force thereto if, for example, thepermeabilities of the fluids are different.

In the particular exemplary embodiment of the invention, depicted inFIG. 3, such a force is provided by the use of an electric field appliedbetween the inner and outer cylindrical members of the apparatus. Whilethe use of electric fields for aiding a static mixing process has beenpreviously suggested, no one has yet suggested the use thereof in adevice which provides vortex-like motions of the fluids involved in amanner such as to create a relatively large number of thin layers of thefluid components to be mixed, such fluids having differentconductivities so that application of the electric field generates ade-stabilizing force, as defined above. In providing for such mixingenhancement by the use of an electric field, the device as shown in FIG.3 has connected to it a source of electrical energy 34 which provides avoltage difference between an outer cylindrical member 20 and an innercylindrical member 21. The electric field can be in the form of a directcurrent field supplied by a suitable DC voltage source or in the form ofan alternating current field supplied by a suitable AC voltage source.If the property difference being exploited is electrical conductivity,the successful use of an AC voltage source requires that 2πf(ε/σ)<1,where f is the frequency of the AC voltage and the ratio (ε/σ) is theshorter electrical relaxation time of the two fluids (ε being thepermittivity thereof and σ being the conductivity thereof). In eithercase, a marked improvement in the mixing effectiveness of the outputproduct mix is achieved when using concentrically mounted inner andouter cylinders in combination with the application of the electricfield as shown in FIG. 3. The voltage level which can be used isessentially limited by the dielectric strengths of the fluid and shouldbe kept at a level below that which would produce dielectric breakdownthereof.

While prior art mixing devices using concentric conical or cylindricalmembers have generally found it desirable to utilize a relatively smallgap region between the inner and outer members, as exemplified by theGurley and Gurley et al patents discussed above, in accordance with theinvention, such gap is made larger than that which has heretofore beenused. Thus, if the gap size is determined in accordance with the ratioa/r in the embodiment of the invention shown in FIG. 3, it has beenfound that good mixing quality has been achieved when such ratio isapproximately 0.5 and it is believed that satisfactory results should beobtained when such ratio lies between about 0.2 and 0.8. In such astructure with fluids having kinematic viscosities for example, lyingwithin the range from about 50 to about 6000 centistokes and usingrotational velocities within the range from about 10,000 r.p.m. to15,000 r.p.m. the resulting vortex-like motion of the fluid componentsproduces an effective and high quality mixing thereof.

While a high quality of mixing effectiveness can be achieved when usinga smooth surfaced inner cylinder together with an applied electricfield, as shown in FIG. 3, the rotational velocities required to achievethe desired vortex-like motion of the fluids for obtaining uniformmixing through region 31 is relatively high. Such motion cannot beachieved unless the critical Taylor number is exceeded as discussedabove. It has been found for example, that the vortex-like motion can beachieved when the Taylor number is above about 41.7 for the structureshown in FIG. 3.

FIG. 4. shows an alternative ambodiment in which the advantages ofvortex-like fluid motion can be achieved substantially independently ofthe value of the Taylor number. The structure therein has an outercylindrical member 40 and a rotatable inner member 41. The latter memberis substantially cylindrical, the surface thereof having a plurality ofV-shaped grooves 42 formed thereon substantially along its length. Afirst input feed line 43 is connected to a first fluid source 44 viapump 45 and valve 46. A second input feed line 47 is connected to asecond fluid source 48 via pump 49 and valve 50. An output feed line 51provides the output product mix.

When the input fluid components are introduced into the region 52between inner and outer members, mixing is accomplished by rotation ofinner member 41. It is found that the presence of V-shaped groovesproduces vortex-like motion of the fluids at much lower rotationalvelocities than that required to produce such motion when using thesmooth inner cylinder of FIG. 3. Such vortex-like motion as showndiagrammatically by vortices 53 appears to be produced substantiallyimmediately when the inner member 41 begins its rotation even atstart-up when the rotation speeds are just above zero r.p.m.

In order to provide for the most effective formation of such vortex-likemotion within the grooves, the mean radius r_(m) of the inner member,the mean gap dimension a_(m) and the groove length L, as shown in FIG.4, can be appropriately selected. As discussed above with the smoothcylinder case, the ratio a_(m) /r_(m) preferably should lie in a rangefrom about 0.4 to about 0.6, with a preferred ratio of about 0.5.Further, it has been found generally that in the configuration shown inFIG. 4, a ratio of gap dimension to groove length (a_(m) /L) of fromabout 0.3 to about 0.7 is effective, with a preferred value therefor ofabout 0.5 in order to provide effective vortex-like fluid movement.

The mixing effectiveness of the structure of FIG. 4 is further enhancedby the application of an electric field to produce a de-stabilizingforce for the fluids which have differing conductivities in the mannerdiscussed above with reference to FIG. 3. Thus, a source of electricenergy 54 provides a voltage difference between the outer member 40 andthe inner member 41 which voltage can be either d-c or a-c voltage, asdiscussed above with reference to FIG. 3. In such case, an effectivelyhigh quality of output mix is provided with the use of relative lowrotational velocities for fluids having viscosities which can range upto about 10³ poise.

An alternative embodiment of the V-shaped construction depicted above isshown in FIG. 5 wherein the V-shaped groove means 62 of inner member 61is formed as a continuous helical groove extending substantially fromone end to the other of inner member 61 which is rotationally mountedwithin outer member 60. The pitch of the groove may lie within a rangefrom about 0.3 to 0.7 with a pitch of about 0.5 being an effective one.In a manner similar to that provided by the use of the independentV-shaped grooves of FIG. 4, such helical V-shaped groove configurationalso provides effective mixing. In using independently formed V-shapedgrooves as shown in FIG. 4, the volume flow rate of the output productmix can be set independently of the speed of rotation of the innermember. In contrast thereto, in the helical groove configuration of FIG.5, the flow rate is dependent upon the speed of rotation and is not setindependently thereof. This fact can be used to regulate the flow rateby changing the speed of rotation.

The V-shaped groove configurations discussed above with reference toFIGS. 4 and 5, can be utilized for either batch or continuous productoutput flow. In the case of a batch process preselected discretequantities of input fluid components are supplied to the mixingapparatus over a preselected period of time and, accordingly, apreselected discrete quantity of output product mix is supplied at theoutput feed line thereof on a discontinuous basis. In a continuousprocess, the inputs are supplied on a continuous basis, the rate ofsupply of input fluid components and the resultant rate of supply ofoutput product mix being appropriately arranged in accordance with adesired production line application. With a configuration as shown inFIG. 4, for example, for viscous fluids such as polyol and isocyanteutilized as the input fluid components thereto, where r_(m) is about 0.7in., a_(m) is about 0.35 in., L is about 0.7 in., and the height h ofthe cylinder is about 3.5 in., the mixing apparatus of the invention caneffectively supply an output product mix as high as about 100 pounds persecond.

In the use of both independent V-shaped grooves and a continuous helicalgroove structure, the formation thereof can be modified somewhat asshown in FIGS. 6 and 7. As seen therein, a plurality of lands 65 areformed at the outer edges of each groove. In some applications, thepresence of such lands appears to tend to further enhance the mixingprocess.

Examples of the effectiveness of the use of an electric field, with andwithout the use of a grooved inner member, as well as the effectivenessof using a grooved inner member, with or without the use of an electricfield, is graphically depicted in FIG. 8. As seen therein, the standarddeviation "S" of the relative concentrations of the two liquids asdetermined from ten separate 1.0 milliliter samples taken from the mixeroutputs is plotted on log-log coordinates against the ratio ω/Q of therotational velocity ω expressed in radians per sec. and the averagevolume flow rate Q of the liquids being mixed expressed in cubiccentimeters per sec. For perfect mixing, the standard derivation Sshould be zero and, hence, the smaller the value of the ordinate, thebetter the mixing illustrated thereby.

In all cases, the two liquids mixed were pure glycerine and dyedgylcerine; the average viscosities thereof being approximately 400centipoises. The rotational velocity in each case was maintained atapproximately 130 radians per second. In those cases wherein an electricfield is used and the conductivities of the fluids are different, theratio of electrical conductivities of the liquids is identified as"C_(R) " in connection with curves 71 and 73 illustrating such use.

As can be seen in FIG. 8, for a mixing apparatus using a smooth innercylinder member of the type shown in FIG. 1 with no electric fieldapplied (i.e., the voltage V=0) the standard deviation curve is depictedby curve 70. When a voltage V equal to 1.7 KV is applied thereto in astructure of the type depicted in FIG. 1, with liquids having aconductivity ratio C_(R) =8, the mixing quality improved considerablyover the range of ω/Q which was used, as shown by curve 71.

Further, the use of a mixing apparatus having a grooved inner cylindermember of the type depicted in FIG. 4, for example, provided a standarddeviation curve as shown by curve 72 when no electric field was applied(i.e., V=0). Such a structure also produced a considerable improvementover the use of a smooth inner cylinder member as seen by comparisonwith curve 70. Moreover, the application of an electric field (by theuse of a voltage V=1.7 KV) provided substantial improvement over themixing produced without the use of such field as well as over anapparatus using a smooth inner cylinder, either with or without anelectric field, as depicted by the standard derivation curve 73. In thelatter case, the ratio of the conductivities C_(R) was equal to 40.

In the case of the mixing apparatus using a smooth inner cylinder forthe results shown by curves 70 and 71, the ratio a/r of the gap "a"between the inner and outer cylinder to the radius "r" of the innercylinder was set at 0.23. In the cases of the mixing apparatus using agrooved inner cylinder for the results shown by curves 72 and 72, theratio a_(m) /r_(m) of the mean gap "a" to the mean raduis r_(m) (seeFIG. 4) was set at 0.47 and the ratio a_(m) /L of the mean gap a_(m) tothe groove length L was set at 0.40, the ratio D/L of the groove depth Dto the groove length L was set at 0.42 and the ratio h/L of the totalheight h of the inner cylinder to the groove length L was set at 5.0.

Although the invention is useful in the mixing of reactive plasticliquid components, such as polyol an isocyanate, the apparatus is notlimited to use therewith and other fluid components may be effectivelymixed in accordance with the spirit and scope of the invention. Further,while the concentric members are described as cylindrical in shape,other configurations may be utilized, such as substantially spherical orconical concentric members, for example. Further, the vortex-like motionof the fluids may be produced by the use of mechanical configurationsother than those using concentrically mounted members as specificallydiscussed herein.

While the particular embodiments shown in the drawings and discussedabove represent preferred embodiments of the invention it is clear thatfurther modifications thereof within the spirit and scope of theinvention may occur to those skilled in the art. Accordingly, theinvention is not to be construed as limited to the specific embodimentsshown except as set forth in the appended claims.

What is claimed is:
 1. A laminar mixing apparatus comprisingan outermember; an inner member concentrically mounted for rotation within saidouter member; means for introducing at least two fluids into the regionbetween said inner and outer members; means for providing a relativerotation between said inner and outer members; groove means formed onthe surface of said inner member, the mean gap dimension between saidinner member and said outer member, the mean distance from the center ofsaid inner member to said groove means, and the length of said groovemeans being selected to produce substantial vortex-like motions of saidfluids in the portions of said region formed between said groove meansand said outer member when said relative rotation is provided, saidfluids thereby being mixed in a substantially laminar fashion by saidgroove means in said region, said groove means tending to prevent theinterface between said fluids from becoming aligned in parallel with thestreamlines of said fluids; and means for removing the mixture of saidfluids from said apparatus.
 2. A mixing apparatus in accordance withclaim 1 wherein said fluids are liquids.
 3. A mixing apparatus inaccordance with claim 2 wherein said liquids have viscosities lyingwithin a range up to about 10³ poise.
 4. A mixing apparatus inaccordance with claim 3 wherein said liquids are liquid plastic resinmaterials.
 5. A mixing apparatus in accordance with claim 4 wherein twoliquid plastic resins are mixed, said first plastic resin being polyoland said second plastic resin being isocyanate.
 6. A mixing apparatus inaccordance with claim 1 wherein said groove means comprise a pluralityof independent V-shaped grooves, said vortex-like motions being producedin the region between said V-shaped grooves and said outer member.
 7. Amixing apparatus in accordance with claim 6 wherein the ratio D/L of thedepth D, of each of V-shaped grooves to the length, L, of each of saidV-shaped grooves lies within a range from about 0.3 to about 0.7.
 8. Amixing apparatus in accordance with claim 7 wherein the ratio of D/L isabout 0.4.
 9. A mixing apparatus in accordance with claim 6, wherein atleast two oppositely-directed vortex-like motions of said fluids occurswithin the portion of said region formed by each of said V-shapedgrooves.
 10. A mixing apparatus in accordance with claim 6 wherein eachof the outer edges of said V-shaped grooves has a land formed thereon.11. A mixing apparatus in accordance with claim 1 wherein said outermember is substantially cylindrical and said inner member comprises aplurality of frusto-conical portions which form a plurality ofindependent V-shaped grooves, said vortex-like motions being produced inthe region between said V-shaped grooves and said outer cylindricalmember and wherein the ratio a_(m) /r_(m) lies within a range from about0.4 to about 0.6, a_(m) being the mean gap dimension between the innermember and the outer cylindrical member and r_(m) being the meandistance from the center of said inner member to said V-shaped grooves.12. A mixing apparatus in accordance with claim 11 wherein the ratioa_(m) /r_(m) is about 0.5.
 13. A mixing apparatus in accordance withclaim 1 wherein said outer member is substantially cylindrical and saidinner member comprises a plurality of frusto-conical portions which forma plurality of independent V-shaped grooves, said vortex-like motionsbeing produced in the region between said V-shaped grooves and saidouter cylindrical member and wherein the ratio a_(m) /L lies in a rangefrom about 0.3 to about 0.7, a_(m) being the mean gap dimension betweenthe inner member and the outer cylindrical member and L being the lengthof each of said V-shaped grooves.
 14. A mixing apparatus in accordancewith claim 13 wherein the ratio a_(m) /L is about 0.4.
 15. A mixingapparatus in accordance with claim 1 wherein said groove means comprisesa continuous helical V-shaped groove extending substantially along thelength of said inner member.
 16. A mixing apparatus in accordance withclaim 15 wherein the pitch of said helical groove lies within a rangefrom about 0.3 to about 0.7.
 17. A mixing apparatus in accordance withclaim 16 wherein said pitch is about 0.5.
 18. A mixing apparatus inaccordance with claim 15 wherein the ratio a_(m) /r_(m) lies in a rangefrom about 0.4 to about 0.6, a_(m) being the mean gap dimension betweenthe inner member and the outer member and r_(m) being the mean distancefrom the center of said inner member to said helical groove.
 19. Amixing apparatus in accordance with claim 18 wherein the ratio a_(m)/r_(m) is about 0.5.
 20. A mixing apparatus in accordance with claim 15wherein the outer edge of said continuous helical groove has a landformed thereon.